Technical Field
The present disclosure relates to a method for modifying nanodiamonds. More particularly, the present disclosure relates to a thiolation method for modifying nanodiamonds.
Description of Related Art
Nanotechnology has been widely applied to many fields, such as surface science, material, semiconductor or drug delivery. The application of nanoscale materials or devices in diagnosis or treatment of diseases is termed nanomedicine. Among developed nanoscale materials, nanodiamonds (ND) exhibit excellent physical and chemical properties, biocompatibility and low toxicity, and are thus regarded as a promising candidate material for nanomedicine and has received considerable attention.
The nanodiamonds can be synthesized by a detonation method. Specifically, a mixture of trinitrotoluene (TNT) and hexogen is exploded in a closed metallic chamber, and a carbon-containing material, such as graphite or carbon nanotube, is transformed into the nanodiamonds by a shock wave.
It is proved that the nanodiamonds be applied to drug delivery applications, can be conjugated with amino acids or DNA as biomarkers or tracers according to specific purposes, and also can be conjugated with fluorescein and magnetic resonance aging (MRI) contrast agents for enhancing image quality.
To achieve the above applications, surfaces of the nanodiamonds are usually modified for generating hydrophilic functional groups thereon. For an example, the surfaces of the nanodiamonds can be oxidized by an acid or ozone (O3) for generating carboxyl groups (COOH) on the surfaces of the nanodiamonds. The carboxyl groups can be further transformed into carboxyl chloride groups (COCl) or hydroxyl groups (OH).
Thiol groups (SH) can be found in proteins and antibodies. A number of the thiol groups in the proteins and the antibodies is lower than that of carboxyl groups or amino groups. Therefore, by using the thiol groups to conjugate with target molecules, numbers and positions of modification sites can be controlled. Moreover, the thiol groups exhibit a strong affinity for gold and thus can be applied to conjugate with gold nanoparticles. Gold nanoparticles have been successfully applied to biological detections, specimen analyses and developers of computed tomography (CT) scan. If the nanodiamonds can be modified with thiol groups, the applications of the nanodiamonds in nanomedicine can be broadened.
The surfaces of the nanodiamonds can be modified with thiol groups by methods as follows. In a first method, the thiol groups can be conjugated on the surfaces of the nanodiamonds via space linkers. In a second method, elemental sulfur and carbon disulfide are provided for modifying the nanodiamonds via a photochemical reaction. However, in the first method, the thiol groups are not directly conjugated on the surfaces of the nanodiamonds. As a result, physical properties of the nanodiamonds may be affected by the space linkers, and a conductivity or applications thereof may be affected. In the second method, a specific equipment is required for the photochemical reaction. The specific equipment is expensive. Accordingly, it is unfavorable to apply the second method to mass production and the production cost thereof remains high.
Therefore, how to directly modify the surfaces of the nanodiamonds with thiol groups, which is favorable to apply to mass production and has low production cost, has become an important goal of relevant academia and industry.